The present disclosure relates to a semiconductor device.
A semiconductor device having a function corresponding to a desired usage is manufactured by using semiconductors having different physical properties for respective regions of the semiconductor device. Physical properties such as band gap, refractive index, etc. are important for designing a device. Such physical properties of semiconductors may be adjusted to desirable values by changing materials, a type and concentration of doped impurities, combinations thereof and the like of layered semiconductors.
One way of altering the physical properties is disordering a semiconductor. As a method of the disordering, there is known an impurity free vacancy disordering (IFVD) method that disorders a semiconductor by diffusing an atomic vacancy by a rapid thermal anneal (RTA) method. For example, this method is used for manufacturing a semiconductor laser device. In a semiconductor laser device, heat may be generated by absorption of laser light at a facet when an optical output increases. In this case, a phenomenon called catastrophic optical damage (COD) may possibly occur, in which the laser device would not function because the facet is melted by the generated heat, and thus it will be a problem of reliability. To solve the problem, a facet transparentization technology by disordering is disclosed, and it is possible to raise the optical output limit, beyond which the COD occurs, by employing this technology.
The facet transparentization technology by disordering is a technology in which, by enlarging band gap energy of a semiconductor region in the vicinity of a facet of a semiconductor device by disordering the semiconductor region, the vicinity of the facet is transparentized for a light emission wavelength to suppress absorption of a laser light (see, for example, Japanese Laid-open Patent Publication No. 2007-242718, Japanese Laid-open Patent Publication No. 9-23037, Japanese Laid-open Patent Publication No. 10-200190, Japanese Laid-open Patent Publication No. 2001-15859, and Japanese Laid-open Patent Publication No. 2011-103494). The transparentized region is called a window region. A region not transparentized is called a non-window region.
In addition, a technology is proposed, which realizes a semiconductor optical device having various functions by varying disordering of regions extending in a layered direction of a semiconductor (see, for example, Japanese Laid-open Patent Publication No. 6-77596).
An example of the disordering by the atomic vacancy diffusion will be explained. FIG. 26 illustrates a vicinity of a facet of a semiconductor device under manufacturing process for explaining the example of the disordering by the atomic vacancy diffusion. As illustrated in FIG. 26, a semiconductor layer to be disordered includes: a substrate (not illustrated in the drawing); an active layer formed thereon; a p-type cladding layer 1012 containing a p-type impurity and formed on the active layer to sandwich a p-type cladding layer; a first impurity layer 1013 doped with a first impurity having a function of accelerating diffusion of an atomic vacancy, the first impurity layer 1013 having high conductivity and functioning as a contact layer; and a second impurity layer 1020 formed in a region (right side of a dashed line in FIG. 26) to be a non-window region on the first impurity layer 1013 and doped with a second impurity having a function of suppressing diffusion of the atomic vacancy. When disordering, a dielectric film 1021 functioning as a suppression film suppressing the disordering is formed on the second impurity layer 1020. Moreover, on an entire surface of the dielectric film 1021, a dielectric film 1022 functioning as an acceleration film accelerating the disordering is formed. By performing the RTA in this state, the atomic vacancy in the region to be the window region is diffused to disorder the semiconductor layer, and thus, the window region and the non-window region are formed.
In this state, a gap is formed at a border portion between each dielectric film and each semiconductor layer, for example, at a border i100 between the dielectric film 1021 and the dielectric film 1022 in FIG. 26, and a region where a semiconductor layer surface is not covered with the dielectric film 1022 may be formed. When performing the RTA with such region, a surface roughness may be formed in the region.
Moreover, a case is considered in which a laser device is manufactured with a semiconductor layer having surface roughness. FIG. 27 is a view for explaining an example of a semiconductor laser device having surface roughness and illustrating a vicinity of a facet of the semiconductor laser device. The semiconductor laser device illustrated in FIG. 27 is manufactured by removing an upper portion of the semiconductor laser device under the manufacturing process illustrated in FIG. 26 by etching, and forming thereon an insulation film 1016 and an upper electrode 1017. Moreover, this semiconductor laser device emits laser by an optical cavity formed by a low reflectivity film 1002 formed on a light-emitting facet side and a high reflectivity film (not illustrated in the drawings) formed on a rear facet side opposing to the light-emitting facet side. It is supposed that a surface roughness r100 is formed in this state of the first impurity layer 1013.
In order to drive this semiconductor laser device, an electric current is injected from the upper electrode 1017. Then, the injected electric current flows downward via the first impurity layer 1013 and flows in the highly conductive first impurity layer 1013 in a horizontal direction. Then, the electric current flowing in the first impurity layer 1013 reaches the surface roughness r100. When energy of the electric current is applied to the surface roughness r100, a dislocation is generated at the surface roughness r100 as an origination, and progresses to an active layer on an electric-current-injection side, that is, a region of the active layer below the upper electrode 1017. There is a problem that, when the dislocation reaches the active layer on the electric-current-injection side, the dislocation grows rapidly by the energy applied to the active layer by the electric current injection, and a dislocation loop is formed, thus the semiconductor laser device is deteriorated. In this case, the surface roughness r100 existing in the vicinity of the border between the window region and the non-window region is an origination of a failure mode.